Method for sizing polytretrafluoroethylene fabrics

ABSTRACT

The invention is a method for sizing polytetrafluoroethylene fabrics comprising: 
     (a) forming a sizing composition of a perfluorinated polymer containing sites convertible to ion exchange groups and a treating agent having: a boiling point less than about 110° C.; a density of from about 1.55 to about 2.2; and a solubility parameter of from greater than about 7.1 to about 8.2 hildebrands; 
     (b) contacting the sizing composition with the fibers of a polytetrafluoroethylene fabric; and 
     (c) removing the treating agent from the sizing composition. 
     Particularly preferred as a treating agent is a compound represented by the general formula: 
     
         XCF.sub.2 -CYZX&#39; 
    
     wherein: 
     X is selected from the group consisting of F, Cl, Br, and I; 
     X&#39; is selected from the group consisting of Cl, Br, and I; 
     Y and Z are independently selected from the group consisting of H, F, Cl, Br, I and R&#39;; 
     R&#39; is selected from the group of perflluoroalkyl radicals and chloroperfluoroalkyl radicals having from 1 to 6 carbon atoms. 
     The most preferred treating agent is 1,2-dibromotetrafluoroethane.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 739,956, filed May 31,1985, now U.S. Pat. No. 4,650,711.

The present invention is a method for sizing polytetrafluoroethylenefabric and particularly a method for sizing polytetrafluoroethylenefabric using a perfluorinated polymer solution or a perfluorinateddispersion.

BACKGROUND OF THE INVENTION

Polytetrafluoroethylene fabrics are fabrics woven from strands ofpolytetrafluoroethylene. Polytetrafluoroethylene is commonly known asTeflon and is a registered trademark of E.I. DuPont Company.

Polytetrafluoroethylene fabrics are available in many varieties from avariety of distributors. Typical of the polytetrafluoroethylene fabricsis a fabric sold by Stern and Stern Textiles, Incorporated, New York,N.Y., called T41-30. It is a lenoweave cloth with 45×21 ends/inch andhas a thickness of 0.010 inch. It has a weight of 4.35 ounces per squareyard.

Polytetrafluoroethylene fabrics are used for a variety of purposesincluding such things as filters, screens, reinforcement, packing,insulation, liners and gasket materials.

They are also used as supports for fluoropolymer ion exchange activefilms. Such fims are commonly used as ion exchange membranes inelectrolytic cells.

Fluoropolymer fabrics are limp and exhibit low friction, thread tothread. This causes these fabrics to become distorted under normalhandling and causes holes to appear without breaking threads.

The prior art has attempted to coat polytetrafluoroethylene fabrics byusing mechanical lamination equipment. Other prior art has attempted toattach polytetrafluoroethylene fabrics to ion exchange membrane filmsusing heat treatment and extraction procedures rather than stabilizingthe cloth itself (see U.S. Pat. No. 4,272,560).

Other known relevant art is known to include: U.S. Pat. Nos. 3,770,567;3,925,135; 4,272,560; 4,324,606; 4,399,183; 4,341,605; and 4,437,951.

Burrell states the theory of Bagley [J. Paint Tech., Volume 41, page 495(1969)] predicts a non-crystalline polymer will dissolve in a solvent ofsimilar solubility parameter without chemical similarity, association,or any intermolecular force. However, he fails to mention anything aboutthe solubility of polymers demonstrating crystallinity.

It would be highly desirable to be able to size polytetrafluoroethylenefabrics. The present invention provides such a method.

SUMMARY OF THE INVENTION

The invention is a method for sizing polytetrafluoroethylene fabricscomprising:

(a) forming a sizing composition of a perfluorinated polymer containingsites convertible to ion exchange groups and a treating agent having:

a boiling point less than about 110° C.;

a density of from about 1.55 to about 2.97 grams per cubic centimeter;and

a solubility parameter of from greater than about 7.1 to about 8.2hildebrands;

(b) contacting the sizing composition with the fibers of apolytetrafluoroethylene fabric; and

(c) removing the treating agent from the sizing composition.

Particularly preferred as a treating agent is a compound represented bythe general formula:

    XCF.sub.2 --CYZX'

wherein:

X is selected from the group consisting of F, Cl, Br, and I;

X' is selected from the group consisting of Cl, Br, and I;

Y and Z are independently selected from the group consisting of H, F,Cl, Br, I and R';

R' is selected from the group of perfluoroalkyl radicals andchloroperfluoroalkyl radicals having from 1 to 6 carbon atoms.

The most preferred treating agent is 1,2-dibromotetrafluoroethane.

DETAILED DESCRIPTION OF THE INVENTION

"Sizing composition" is a composition containing a treating agent and aperfluorinated polymer containing sites convertible to ion exchangegroups, wherein the polymer is at least partially dissolved in thetreating agent.

Polytetrafluoroethylene fabrics are limp cloths before sizing. Thethreads usually tend to slide about during handling and are, thus, verydifficult to handle without changing the shape of the fabric. Thepresent invention provides a method for sizing polytetrafluoroethylenefabrics.

Polytetrafluoroethylene fabrics suitable for use in the presentinvention are those commercially available from a variety of producers.The denier of the fabric is not critical to the successful operation ofthe present process. Likewise, the overall physical dimensions of thefabrics are not critical.

Polytetrafluoroethylene fabrics are treated with a solution ordispersion of a treating agent and a perfluorinated polymer.

Non-ionic forms of perfluorinated polymers described in the followingpatents are suitable for use in the present invention: U.S. Pat. Nos.3,282,875; 3,909,378; 4,025,405; 4,065,366; 4,116,888; 4,123,336;4,126,588; 4,151,052; 4,176,215; 4,178,218; 4,192,725; 4,209,635;4,212,713; 4,251,333; 4,270,996; 4,329,435; 4,330,654; 4,337,137;4,337,211; 4,340,680; 4,357,218; 4,358,412; 4,358,545; 4,417,969;4,462,877; 4,470,889; and 4,478,695; European Patent Application0,027,009. Such polymers have equivalent weights from about 500 to about2000.

Particularly preferred are copolymers of monomer I with monomer II (asdefined below). Optionally, a third type of monomer may be copolymerizedwith I and II.

The first type of monomer is represented by the general formula:

    CF.sub.2 =CZZ'                                             (I)

wherein:

Z and Z' are independently selected from the group consisting of --H,--Cl, --F, or CF₃.

The second monomer consists of one or more monomers selected fromcompounds represented by the general formula:

    Y--(CF.sub.2).sub.a --(CFR.sub.f).sub.b --(CFR.sub.f').sub.c --O--[CF(CF.sub.2 X)--CF.sub.2 --O].sub.n --CF=CF.sub.2   (II)

where:

Y is selected from the group consisting of --SO₂ Z, --CN, --COZ, andC(R³ _(f))(R⁴ _(f))OH;

Z is I, Br, Cl, F, Or or NR₁ R₂ ;

R is a branched or linear alkyl radical having from 1 to about 10 carbonatoms or an aryl radical;

R³ _(f) and R⁴ _(f) independently selected from the group consisting ofperfluoroalkyl radicals having from 1 to about 10 carbon atoms;

R₁ and R₂ are independently selected from the group consisting of H, abranched or linear alkyl radical having from 1 to about 10 carbon atomsor an aryl radical;

a is 0-6;

b is 0-6;

c is 0 or 1;

provided a+b+c is not equal to 0;

X is Cl, Br, F or mixtures thereof when n>1;

n is 0 to 6; and

R_(f) and R_(f') are independently selected from the group consisting ofF, Cl, perfluoroalkyl radicals having from 1 to about 10 carbon atomsand fluorochloroalkyl radicals having from 1 to about 10 carbon atoms.

Particularly preferred is when Y is --SO₂ F or --COOCH₃ ; n is 0 or 1;R_(f) and R_(f') are F; X is Cl or F; and a+b+c is 2 or 3.

The third and optional monomer suitable is one or more monomers selectedfrom the compounds represented by the general formula:

    Y'--(CF.sub.2).sub.a' --(CFR.sub.f).sub.b' --(CFR'.sub.f).sub.c' --O--[CF(CF.sub.2 X')--CF .sub.2 --O)].sub.n' --CF=CF.sub.2 (III)

where:

Y' is F, Cl or Br;

a' and b' are independently 0-3;

c' is 0 or 1;

provided a'+b'+c' is not equal to 0;

n' is 0-6;

R_(f) and R'_(f) are independently selected from the group consisting ofBr, Cl, F, perfluoroalkyl radicals having from about 1 to about 10carbon atoms, and chloroperfluoroalkyl radicals having from about 1 toabout 10 carbon atoms; and

X' is F, Cl, Br, or mixtures thereof when n'>1.

Conversion of Y to ion exchange groups is well known in the art andconsists of reaction with an alkaline solution.

The monomer FSO₂ CF₂ CF₂ OCF=CF₂ has a density of about 1.65 grams percubic centimeter and polytetrafluoroethylene has a density of about 2.2grams per cubic centimeter. A copolymer of this monomer withtetrafluoroethylene would, thus, have a density between the two values.

It has been discovered that certain perhalogenated treating agents havea surprising effect of dissolving and dispersing the polymers,especially when the polymers are in a finely divided state.

Treating agents suitable for use in the present invention to form thesizing compositions of the present invention preferably have thefollowing characteristics:

a boiling point less than about 110° C.;

a density of from about 1.55 to about 2.97 grams per cubic centimeter;

a solubility parameter of from greater than about 7.1 to about 8.2hildebrands.

It is desirable that the treating agents have a boiling point of fromabout 30° C. to about 110° C. The ease of removal of the treating agentand the degree of treating agent removal is important in the producingof various films, coatings and the like, without residual treatingagent; hence a reasonable boiling point at atmospheric pressure allowsconvenient handling at room conditions yet effective treating agentremoval by atmospheric drying or mild warming.

It is desirable that the treating agent has a density of from about 1.55to about 2.97 grams per cubic centimeter. The polymers of the presentinvention have densities on the order of from about 1.55 to about 2.2grams per cubic centimeter. Primarily, the polymers have densities inthe range of from abcut 1.6 to about 2.2 grams per cubic centimeter.Treating agents of the present invention will therefore swell dissolveand disperse small particles of this polymer, aided by the suspendingeffects of the similarity in densities.

The prior art did not balance density. They were interested in formingsolutions and solutions do not separate.

Solubility parameters are related to the cohesive energy density ofcompounds. Calculating solubility parameters is discussed in U.S. Pat.No. 4,348,310, the teachings of which are incorporated by reference forthe purpose of their teachings about solubility parameters.

It is desirable that the treating agent has a solubility parameter offrom greater than about 7.1 to about 8.2 hildebrands. The similarity incohesive energy densities between the treating agent and the polymerdetermine the likelihood of dissolving, swelling or dispersing thepolymer in the treating agent.

It is desirable that the treating agent has a vapor pressure of up toabout 760 millimeters of mercury at the specified temperature limits atthe point of treating agent removal. The treating agent should beconveniently removed without the necessity of higher temperatures orreduced pressures involving extended heating such as would be necessaryin cases similar to U.S. Pat. No. 3,692,569 or the examples in Britishpatent No. 2,066,824A in which low pressures (300 millimeters) had to beemployed as well as non-solvents to compensate for the higher boilingpoints and low vapor pressures of the complex solvents.

It has been found that treating agents represented by the followinggeneral formula are particularly preferred provided they also meet thecharacteristics discussed above (boiling point, density, and solubilityparameter):

    XCF.sub.2 --CYZ--X'

wherein:

X is selected from the group consisting of F, Cl, Br, and I;

X' is selected from the group consisting of Cl, Br, and I;

Y and Z are independently selected from the group consisting of H, F,Cl, Br, I and R';

R' is selected from the group of perfluoroalkyl radicals andchloroperfluoroalkyl radicals having from 1 to 6 carbon atoms.

The most preferred treating agents are 1,2-dibromotetrafluoroethane(commonly known as Freon 114 B 2)

    BrCF.sub.2 --CF.sub.2 Br

and 1,2,3-trichlorotrifluoroethane (commonly known as Freon 113):

    ClF.sub.2 C--CCl.sub.2 F

Of these two treating agents, 1,2-dibromotetrafluoroethane is the mostpreferred treating agent. It has a boiling point of about 47.3° C., adensity of about 2.156 grams per cubic centimeter, and a solubilityparameter of about 7.2 hildebrands.

1,2-dibromotetrafluoroethane is thought to work particularly wellbecause, though not directly polar, it is highly polarizable. Thus, when1,2-dibromotetrafluoroethane is associated with a polar molecule, itselectron density shifts and causes it to behave as a polar molecule.Yet, when 1,2-dibromotetrafluoroethane is around a non-polar molecule,it behaves as a non-polar treating agent. Thus,1,2-dibromotetrafluoroethane tends to dissolve the non-polar backbone ofpolytetrafluoroethylene and also the polar, ion-exchange-containingpendant groups. The solubility of 1,2-dibromotetrafluoroethylene iscalculated to be from about 7.13 to about 7.28 hildebrands.

It is surprising that an off-the-shelf, readily-available compound suchas 1,2-dibromotetrafluoroethane would act as a solvent for thefluoropolymers described above. It is even more surprising that1,2-dibromotetrafluoroethane happens to have a boiling point, a densityand a solubility parameter such that it is particularly suitable for useas a solvent/dispersant in the present invention.

In practicing the present invention, the polymer may be in any physicalform. However, it is preferably in the form of fine particles to speeddissolution and dispersion of the particles into the treating agent.Preferably, the particle size of the polymers is from about 0.01 micronsto about 840 microns. Most preferably, the particle size is less thanabout 250 microns.

To dissolve and disperse the polymer particles into the treating agent,the polymer particles are placed in contact with the treating agent ofchoice and intimately mixed. The polymer and the treating agent may bemixed by any of several means including, but not limited to, shaking,stirring, milling or ultra sonic means. Thorough, intimate contactbetween the polymer and the treating agent are needed for optimumdissolution and dispersion.

The polymers of the present invention are dissolved and dispersed intothe treating agents at concentrations ranging from about 0.1 to about 50weight percent of polymer to treating agent. At concentrations belowabout 0.1 weight percent, there is insufficient polymer dissolved anddispersed to be effective as a medium for coating of articles or formingfilms within a reasonable number of repetitive operations. Conversely,at concentrations above about 50 weight percent there is sufficientpolymer present as a separate phase such that viable, coherent films andcoatings of uniform structure cannot be formed without particulateagglomerates, etc.

Preferably, the concentration of the polymer in the treating agent isfrom about 0.1 to about 20 weight percent. More preferably, theconcentration of the polymer in the treating agent is from about 0.3 toabout 10 weight percent. Most preferably, it is from about 5 to about 15weight percent.

Dispersing the polymer into the treating agent can be conducted at roomtemperature conditions. However, the optimum dispersing effects are bestachieved at temperatures from about 10° C. to about 50° C. Attemperatures above about 50° C. the measures for dissolving anddispersing the polymer have to include pressure confinement for thepreferred treating agents or method of condensing the treating agents.Conversely, at temperatures below about 10° C., many of the polymers ofthe present invention are below their glass transition temperatures thuscausing their dispersions to be difficult to form at reasonableconditions of mixing, stirring, or grinding.

The sizing composition of the present invention into the treating agentare best conducted at atmospheric pressure. However, dispersing effectscan be achieved at pressures from about 760 to about 15,000 millimetersmercury or greater. At pressures below about 760 millimeters mercury,the operation of the apparatus presents no advantage in dissolving anddispersing polymers, rather hindering permeation into the polymers andthus preventing forming of the sizing compositions.

Conversely, pressures above about 760 millimeters mercury aid indissolving and dispersing polymers very little compared to thedifficulty and complexity of the operation. Experiments have shown thatat about 20 atmospheres the amount of polymer dissolved and dispersed inthe treating agent is not appreciably greater.

The following methods are suitable for fixing the sizing composition ofthe present invention to a polytetrafluoroethylene fabric. Dipping thefabric into the sizing composition, followed by air drying and sinteringat the desired temperature with sufficient repetition to build thedesired thickness. Spraying the sizing composition onto the fabric isused to advantage for covering large or irregular shapes. Pouring thesizing composition onto the fabric is sometimes used. Painting thesizing composition with brush or roller has been successfully employed.In addition, coatings may be easily applied with metering bars, knivesor rods. Usually, the coatings or films are built up to the thicknessdesired by repetitive drying and sintering.

The fabric upon which the sizing composition is to be deposited iscleaned or treated in such a way as to assure uniform contact with thesizing composition. The fabric can be cleansed by washing with adegreaser or similar solution followed by drying to remove any dust oroils from the fabric.

After being cleaned, the fabrics may be pre-conditioned by heating orvacuum drying prior to contact with the sizing compositions and thecoating operation. Temperatures and pressures in the following rangesare preferably used: about 20 millimeters mercury at about 110° C. orthereabout is sufficient in all cases; however, mild heat is usuallyadequate, on the order of about 50° C. at atmospheric pressure.

After preparation, the fabrics are coated with the sizing composition byany of several means including, but not limited to, dipping, spraying,brushing, pouring. Then the sizing composition may be evened out usingscraping knives, rods, or other suitable means. The sizing compositioncan be applied in a single step or in several steps depending on theconcentration of the polymer in the sizing composition and the desiredthickness of the coating.

Following the application of the sizing composition, the treating agentis removed by any of several methods including, but not limited to,evaporation or extraction. Extraction is the use of some agent whichselectively dissolves or mixes with the treating agent but not thepolymer.

These removal means should be employed until a uniform deposition ofpolymer is obtained.

The treating agent removal is typically carried out by maintaining thecoated substrate at temperatures ranging from about 10° C. to about 110°C., with the preferred heating range being from about 20° C. to about100° C. The heating temperature selected depends upon the boiling pointof the treating agent.

Heating temperatures are customarily in the range of from about 20° C.to about 50° C. for 1,2-dibromo-tetrafluoroethane.

The pressures employed for the removal of the treating agent from thecoated substrate can range from about 20 mm mercury to about 760 mmmercury depending on the nature of the treating agent, althoughpressures are typically in the range of from about 300 mm mercury toabout 760 mm mercury for 1,2-dibromotetrafluoroethane.

The forming of the coating can be carried out as part of the polymerdeposition and treating agent removal process or as a separate step byadjusting the thermal and pressure conditions associated with theseparation of the polymer from the sizing composition. If the sizingcomposition is laid down in successive steps, a coating can be formedwithout any subsequent heating above ambient temperature by control ofthe rate of evaporation. This can be done by vapor/liquid equilibrium ina container or an enclosure; therefore, the treating agent removal stepcan be merely a drying step or a controlled process for forming acoating.

After the treating agent has been removed, the residual polymer, as aseparate step, is preferably subjected to a heat source of from about250° C. to about 320° C. for times ranging from about 10 seconds toabout 120 minutes, depending upon the thermoplastic properties of thepolymers. The polymers having melt viscosities on the order of 5×10⁵poise at about 300° C. at a shear rate of 1 sec.⁻¹ as measured by atypical capillary rheometer would require the longer times and highertemperatures within the limits of the chemical group stability. Polymerswith viscosities on the order of 1 poise at ambient temperatures wouldrequire no further treatment.

The most preferred treatment temperatures are from about 270° C. toabout 320° C. and a time of from about 0.2 to about 45 minutes for themost preferred polymers for use in the present invention. Such polymerspermeate the fabric under the conditions described above.

A use for the present invention is the preparation of impregnated orpolymer-permeated reinforcement media which may be used to supportmembrane films. Reinforcement scrims or cloths may be prepared bydipping, painting or spraying the sizing compositions onto the scrim orcloth. Then, the coated scrim or cloth is baked or sintered to fix thefluoropolymer impregnation to the scrim or cloth. The impregnated scrimor cloth is easier to handle than untreated scrims or cloths.

EXAMPLES Example 1

A oopolymer of CF₂ ═CF₂ and CF₂ ═CFOCF₂ CF₂ SO₂ F having equivalentweight of about 850. The polymer was prepared according to the followingprocedure. About 784 grams of CF₂ ═CFOCF₂ CF₂ SO₂ F was added to about4700 grams of deoxygenated water containing about 25 grams NH₄ O₂ CC₇F₁₅, about 18.9 grams of Na₂ HPO₄. 7H₂ O, about 15.6 grams of NaH₂PO₄.H₂ O and about 4 grams of (NH₄)₂ S₂ O₈ under a positive pressure ofabout 192 pounds per square inch gauge (psig) of tetrafluoroethylene atabout 60° C. for about 88 minutes. The reactor was vented under heat andvacuum to remove residual monomers. The reactor contents was frozen,thawed, and vigorously washed to remove residual salts and soap. Aftervacuum drying, a sizing solution was prepared by placing 35 grams ofpolymer prepared above in a laboratory-size single tier 290 revolutionsper minute roller Norton Jar Mill with 315 grams of1,2-dibromotetrafluoroethane. The mixture was mixed in the ball millovernight at ambient temperature and at atmospheric pressure. Thedispersant was analyzed and found to contact about 10 weight percentsolids.

To the resulting soft paste about 300 additional grams of1,2-dibromotetrafluoroethane was added and the mill was rolled anadditional 3 hours. The resulting dispersion was found to contain about10 weight percent polymer.

A circle of Prodesco polytetrafluoroethylene cloth 24×24 leno weaveabout six inches in diameter was cut from a supply ofpolytetrafluoroethylene cloth. It was clamped into a hoop. The hoop andpolytetrafluoroethylene cloth was dippened into the sizing oompositionprepared above. The hoop was removed from the sizing composition and theexcess sizing composition was shaken off. After being allowed to airdry, the coated polytetrafluoroethylene cloth was placed in a mufflefurnace and kept at about 225° C. for about 1 minute.

The sized polytetrafluoroethylene cloth had been well permeated with thesizing composition and had a good "hand" (as used in textileterminology), compared to the limp cloth before the sizing treatment.The threads, which usually tend to slide about during handling, werethen effectively held in place and the polytetrafluoroethylene cloth waseasily removed from the hoop.

We claim:
 1. A method for sizing polytetrafluoroethylene fabricscomprising:(a) contacting a polytetrafluoroethylene fabric with a sizingcomposition of a perfluorinated polymer containing sites convertible toion exchange groups and a treating agent having: a boiling point lessthan about 110° C.; a density of from about 1.55 to about 2.97 grams percubic centimeter; and a solubility parameter of from greater than about7.1 to about 8.2 hildebrands; and (b) removing the treating agent fromthe sizing composition thereby depositing the perfluorinated polymeronto the surface of the polytetrafluoroethylene fabric.
 2. The method ofclaim 1 wherein the perfluorinated polymer is a copolymer of a firsttype of monomer and a second type of monomer;wherein the first type ofmonomer is represented by the general formula:

    CF.sub.2 ═CZZ'                                         (I)

where: Z and Z' are independently selected from the group consisting of--H, --Cl, --F, or CF₃ ;

    Y--(CF.sub.2).sub.a --(CFR.sub.f).sub.b --(CFR.sub.f').sub.c --O--[CF(CF.sub.2 X)--CF.sub.2 --].sub.n --CF═CF.sub.2 (II)

where: Y is selected from the group consisting of --SO₂ Z, --CN, --COZ,and C(R³ _(f))(R⁴ _(f))OH; Z is I, Br, Cl, F, Or or NR₁ R₂ ; R is abranched or linear alkyl radical having from 1 to about 10 carbon atomsor an aryl radical; R_(f) ³ and R_(f) ⁴ are independ ently selected fromthe group consisting of perfluoroalkyl radicals having from 1 to about10 carbon atoms; R₁ and R₂ are independently selected from the groupconsisting of H, a branched or linear alkyl radical having from 1 toabout 10 carbon atoms or an aryl radical; a is 0-6; b is 0-6; c is 0 or1; provided a+b+c is not equal to 0; X is Cl, Br, F or mixtures thereofwhen n>1; n is 0 to 6; and R_(f) and R_(f') are independently selectedfrom the group consisting of F, Cl, perfluoroalkyl radicals having from1 to about 10 carbon atoms and fluorochloroalkyl radicals having from 1to about 10 carbon atoms.
 3. The method of claim 2 wherein theperfluorinated polymer is a copolymer formed from three types ofmonomers wherein the third type of monomer is one or more monomersrepresented by the general formula:

    Y'--(CF.sub.2).sub.a' --(CFR.sub.f).sub.b' --(CFR'.sub.f).sub.c' --O--[CF(CF.sub.2 X')--CF.sub.2 --O].sub.n' --CF═CF.sub.2 (III)

where: Y' is F, Cl or Br; a' and b' are independently 0-3; c' is 0 or 1;provided a'+b'+c' is not equal to 0; n' is 0-6; R_(f) and R'_(f) areindependently selected from the group consisting of Br, Cl, F,perfluoroalkyl radicals having from about 1 to about 10 carbon atoms,and chloroperfluoroalkyl radicals having from about 1 to about 10 carbonatoms; and X' is F, Cl, Br, or mixtures thereof when n'>1.
 4. The methodof claim 1 wherein the boiling point of the treating agent is from about30° C. to about 110° C.
 5. The method of claim 1 wherein the density ofthe treating agent is from about 1.55 to about 2.97 grams per cubiccentimeter.
 6. The method of claim 1 wherein the solubility parameter ofthe treating agent is from greater than about 7.1 to about 8.2hildebrands.
 7. The method of claim 1 wherein the density of thetreating agent and the density of the polymer are both from about 1.55to about 2.2 grams per cubic centimeter.
 8. A method for sizingpolytetrafluoroethylene fabrics comprising:(a) contacting apolytetrafluoroethylene fabric with a sizing composition of aperfluorinated polymer containing sites convertible to ion exchangegroups and a treating agent, wherein the treating agent is representedby the general formula:

    XCF.sub.2 --CYZX'

wherein: X is selected from the group consisting of F, Cl, Br, and I; X'is selected from the group consisting of Cl, Br, and I; Y and Z areindependently selected from the group consisting of H, F, Cl, Br, I andR'; R' is selected from the group of perfluoroalkyl radicals andchloroperfluoroalkyl radicals having from 1 to 6 carbon atoms; (b)removing the treating agent from the sizing composition therebydepositing the fluorinated polymer onto the surface of thepolytetrafluoroethylene fabric.
 9. The method of claim 8 wherein X andX' are Br.
 10. The method of claim 8 wherein X and X' are Cl.
 11. Themethod of claim 8 wherein the polymer is present in the sizingcomposition at a concentration of from about 0.1 to about 50 weightpercent.
 12. The method of claim 8 wherein the polymer is present in thesizing composition at a concentration of from about 0.3 to about 30weigt percent.
 13. The method of claim 8 wherein the perfluorinatedpolymer is a copolymer of a first type of monomer and a second type ofmonomer:wherein the first type of monomer is represented by the generalformula:

    CF.sub.2 ═CZZ'                                         (I)

where: Z and Z' are independently selected from the group consisting of--H, --Cl, --F, or CF₃ ; the second type of monomer is a fluorovinylcompound represented by the general formula:

    Y--(CF.sub.2).sub.a --(CFR.sub.f).sub.b --(CFR.sub.f').sub.c --O--[CF(CF.sub.2 X)--CF.sub.2 --O].sub.n --CF═CF.sub.2 (II)

where: Y is selected from the group consisting of --SO₂ Z, --CN, --COZ,and C(R_(f) ³)(R_(f) ⁴)OH; Z is I, Br, Cl, F, Or or NR₁ R₂ ; R is abranched or linear alkyl radical having from 1 to about 10 carbon atomsor an aryl radical; R_(f) ³ and R_(f) ⁴ independently selected from thegroup consisting of perfluoroalkyl radicals having from 1 to about 10carbon atoms; R₁ and R₂ are independently selected from the groupconsisting of H, a branched or linear alkyl radical having from 1 toabout 10 carbon atoms or an aryl radical; a is 0-6; b is 0-6; c is 0 or1; provided a+b+c is not equal to 0; X is Cl, Br, F or mixtures thereofwhen n>1; n is 0 to 6; and R_(f) and R_(f') are independently selectedfrom the group consisting of F, Cl, perfluoroalkyl radicals having from1 to about 10 carbon atoms and fluorochloroalkyl radicals having from 1to about 10 carbon atoms.
 14. The method of claim 8 wherein theperfluorinated polymer is a copolymer formed from three types ofmonomers wherein the third type of monomer is one or more monomersrepresented by the general formula:

    Y'--(CF.sub.2).sub.a' --(CFR.sub.f).sub.b' --(CFR'.sub.f).sub.c' --O--[CF(CF.sub.2 X')--CF.sub.2 --O].sub.n' --CF═CF.sub.2 (III)

where: Y' is F, Cl or Br; a' and b' are independently 0-3; c' is 0 or 1;provided a'+b'+c' is not equal to 0; n' is 0-6; R_(f) and R'_(f) areindependently selected from the group consisting of Br, Cl, F,perfluoroalkyl radicals having from about 1 to about 10 carbon atoms,and chloroperfluoroalkyl radicals having from about 1 to about 10 carbonatoms; andX' is F, Cl, Br, or mixtures thereof when n'>1.
 15. The methodof claim 8 whereY is --SO₂ F or --COOCH₃ ; n is 0 or 1; R_(f) and R_(f')are F; X is Cl or F; and a+b+c=2 or
 3. 16. The sized fabric producedfrom the method of claim
 1. 17. The sized fabric produced from themethod of claim
 2. 18. The sized fabric produced from the method ofclaim
 3. 19. The sized fabric produced from the method of claim
 4. 20.The sized fabric produced from the method of claim
 5. 21. The sizedfabric produced from the method of claim
 6. 22. The sized fabricproduced from the method of claim
 7. 23. The sized fabric produced fromthe method of claim
 8. 24. The sized fabric produced from the method ofclaim
 9. 25. The sized fabric produced from the method of claim
 10. 26.The sized fabric produced from the method of claim
 11. 27. The sizedfabric produced from the method of claim
 12. 28. The sized fabricproduced from the method of claim
 13. 29. The sized fabric produced fromthe method of claim
 14. 30. The sized fabric produced from the method ofclaim
 15. 31. The sized fabric produced from the method of claim 16.